History Undertale / TropesCToF

* DiminishingReturnsForBalance: Using a Punch Card while a Tough Glove is equipped provides +6 to attack. It can be done repeataedly in one fight, but doing so for the third time only grants a +3 bonus, which drops to +2 for each subsequent use.

** In a No Mercy run, [[spoiler:almost every single fight will end with you obliterating the monster with a single strike. The game is intentionally balanced to be challenging to a Frisk at LV 1, ''at their absolute weakest''. There are, however, [[BonusBoss two notable exceptions]] who will ''turn this trope on you'': [[WakeUpCallBoss Undyne]] [[SuperMode the Undying]], and [[AwakeningTheSleepingGiant Sans]]]].

** Against the BonusBoss in the UsefulNotes/NintendoSwitch version, Mad Mew Mew, you have the option of employing this yourself, which gets some LampshadeHanging if you do. [[spoiler:Specifically, Mad Mew Mew asks you to show her what LOVE is. She means literal love, but if you employ the ''other'' meaning of LOVE used throughout the game — which is to say, violence — she remarks, before falling apart, "I suppose I should have expected that."]]

** One is hidden [[spoiler:a few screens before Snowdin. You can unlock it by successfully avoiding the special thanks credits during the true pacifist ending. Sadly, you cannot fight the dog inside...]]

* DrivenToSuicide: The topic is suicide is touched upon in the game, but never directly stated.

** Also a part of [[spoiler: Flowey]]'s backstory. [[spoiler: After awaking as a flower in Asgore's garden, he eventually found that he couldn't feel any love or warmth from his parents. Not wanting to live in a world without love, he committed suicide. The only reason he is still alive is because, during his attempt, he realized he was afraid of actually dying, and that unwillingness to die caused him to wake back up in the garden as though nothing had ever happened. This is how he discovered his ability to save and load.]]
** If you fight Asgore again ([[spoiler:before befriending Alphys]]) and spare him again, [[spoiler: he will kill himself in order for you to take his soul.]]
** [[spoiler:Asriel]] also wonders if this might be [[spoiler:the reason the protagonist climbed Mt. Ebott at the start of the game.]]

** It is implied by two conversations with [[spoiler:Flowey and Asriel]] that the [[spoiler: Fallen Human]] tried to kill themself by climbing Mt.Ebott, due to their hatred of humanity.

--> '''Flowey''': [[spoiler: But I decided it wasn't worth living anymore. I decided to follow your footsteps. I would erase myself from existence.]]

** The demo has some oddities in the combat system that aren't carried over to the final game. Namely, it allows the player to earn EXP by lowering monsters' health before sparing them, while EXP can only be earned by killing them in the final game. [[spoiler:Since EXP stands for Execution Points, it wouldn't make sense to be able to earn any without killing anything.]] Vegetoids in the demo also must be spared by attacking them first, and the "Devour" ACT will kill them outright; in the final game they can be spared through [=ACTs=] like every other monster and "Devour" never harms the Vegetoid.

** A No Mercy run requires you to do much more work than any other run, killing every random encounter in each area (''all'' of them; you won't discover there's a finite amount unless you're a habitual grinder). Other than that, [[SubvertedTrope it is way easier than a neutral or pacifist run]] because [[spoiler:most bosses get one-shotted by your evil and hatred, and several puzzles are solved for you]], but has some ''[[DoubleSubversion tremendous]]'' {{Difficulty Spike}}s in [[spoiler:Undyne the Undying and Sans]]. All this for the worst ending in the game.

* EarnYourHappyEnding: If you spared every enemy and reached the final room with no kills? Not only did you not increase your LV (meaning you beat the game on the starting 20 HP), you still don't get the good ending unless you've befriended everybody. Then after that, you go through the True Lab, and find out the secrets of the hidden lab, as well as the truth of Flowey's existence, followed by another boss battle. The other monsters also get their happy endings:

** Alphys is rightly [[spoiler:fired from her position as Royal Scientist, since she caused all the problems with Flowey and the Amalgamates. She's actually happy about that because it means the burden is no longer on her. Undyne and she start a relationship, complete with smooches]].

** [[spoiler:Mettaton becomes a star, reconciles with Napstablook, and hires Shyren to sing for him as well as Napstablook as a DJ. Burgerpants also finally gets his chance to shine... [[PlayingATree as a tree]]]].

** The Snowdin Shop only sells gloves, bandannas, popsicles and cinnamon rolls.

* {{Egopolis}}: In the Neutral ending where Mettaton becomes the new ruler of the Underground, he turns it into his "personal paradise", filled with statues of him, his name spelled out in flowers, and so on. Under his rule, the Underground suffers from major problems, such as overcrowding and economic collapse, but he keeps the crowds placated with [[BreadAndCircuses his brainwashing TV show and covering everything with glitter]].
* EmpathicEnvironment: The save point immediately before the battle with Undyne reads "The wind is howling. You're filled with determination..." If you kill her, the wind stops, and its message changes accordingly.

* EstablishingSeriesMoment: When you exit the ruins, Flowey will talk to you, his dialogue varying depending on the actions the player takes. [[spoiler: Killing anyone will have him taunt you for it, and if you save Toriel but kill any normal enemies, he will also mention that. In the slightly likely chance you kill Toriel and restart to save her, he'll reveal his knowledge of this and your past murder before leaving.]]

* EverybodyLives: The True Pacifist ending naturally ends with everyone in the Underground alive. In fact, everyone being alive is important to the end of the run; [[spoiler:Flowey has to absorb ''all'' the monsters' [=SOULs=] to gain his maximum power, so killing even the least important of monsters locks you out of it (though the direct reason is that you can't get Undyne's Letter if there have been any casualties). However, the epilogue reveals that Napstablook’s soul wasn’t taken, indicating that not every single soul was needed.]]

** In full force on a No Mercy run. The few characters who can stand up to you will most likely kill you over and over again... [[DeathIsASlapOnTheWrist but you have determination on your side to bring you back from the dead]] and they don't, so unless you reset, they're ultimately fighting a hopeless battle. Likewise, [[spoiler:completing a No Mercy run just once is all the Fallen needs to destroy the world and steal your SOUL, which negatively affects all subsequent True Pacifist playthroughs]].
** {{Inverted|Trope}} in a No Mercy run, as you only have to show Mercy ''once'' to lock yourself out of it. [[note]]Well, technically, you have to not kill a unique monster (read: miniboss, boss, or [[MyFriendsAndZoidberg Snowdrake]]) to lock yourself out of the No Mercy route; you can spare as many [[RandomEncounters generic monsters]] (including Snowdrake) as you want and still complete a No Mercy run as long as you meet your kill quota by the end of each area (and kill all the unique monsters ([[http://i.imgur.com/BfmQHiN.png including Snowdrake]], who you can spare as often as you want as long as you eventually kill him)). [[https://www.youtube.com/watch?v=2uDsUECZLUk/ You can even spare Lesser Dog by never confronting it in the first place]] (which is admittedly [[LuckBasedMission a complete matter of luck]], as you ''do'' have to kill it to continue the No Mercy run if you do meet it in a RandomEncounter), which overall creates a bizarre inversion of WhatMeasureIsAMook.[[/note]] [[spoiler:When you discover the consequences of your murderous playthrough, you might reflect on how you made a ''willing effort'' to bring them about. You could have made that world less miserable ''any'' time you wanted... and it would have been so easy.]]

** The TagLine for the game: "The Friendly [=RPG=] Where Nobody Has To Die." Sure, nobody ''has'' to die...but [[AnyoneCanDie anyone can]].
** One right when you start the game: [[spoiler:"Name the fallen human." They don't tell you ''which'' fallen human you're naming...]]

** At one point, Sans warns you that his brother has a Special Attack. [[spoiler: The first attack Papyrus puts emphasis on in his fight is his ''Blue'' attack, not necessarily his ''special'' attack, which will probably further trick people into thinking Papyrus is all bluster before he turns their SOUL blue.]]

* ExperiencePenalty: If you reduce Napstablook's HP to 0, they reveal they were lowering their HP on purpose to make you feel better, since they can't die on account of already being a ghost. At the end of the fight, you lose 1 experience point. [[spoiler:But the extra-observant may notice that [[InterfaceSpoiler you]] ''[[InterfaceSpoiler don't]]'' [[InterfaceSpoiler lose any EXP...]]]]

** Near the end of the Genocide path, [[spoiler:Flowey appears and talks about how your determination — the power to cheat death — has surpassed even his, then talks about how similar the two of you are in how you're both willing to kill the other if they got in your way. His expression quickly changes from his usual smug self to that of absolute ''horror'' as he puts two and two together...]]

* FakeOutOpening: It's shown that [[spoiler:the opening cutscene isn't the protagonist, Frisk, falling down and entering the underground — rather, it's the Fallen Child who befriended Asriel.]] Subverted a bit in that it's not the game faking you out, necessarily, but rather your own assumptions about how [=RPGs=] work and introduce information, which are then repeatedly tested throughout the game.

** In the Neutral ending, [[spoiler:you have the option to spare Flowey. He not only fails to understand this, but blatantly comments that refusing to put an end to him just means he will continue to torment you and everyone you love. Afterwards, it seems to have somewhat affected him, causing him to reveal the way to get a truly happy ending... only for it to turn out to be a ploy to bring every [=SOUL=] into his grasp. And then subverted — after said [=SOULs=] remind him of what it's like to feel love (not to mention making him capable of actually feeling it again), he immediately throws out his previous plans of destroying the world in favor of a StableTimeLoop that will allow him to play with you forever, then throws ''that'' plan out once he realizes he's being selfish and self-defeating. Even after he releases the [=SOULs=] and returns to his original state, he shows remorse for what happened despite his returned lack of love.]]

** Undyne is a female example. She makes it very clear how much she cares about Papyrus, though the relationship is more similar to brother and sister than mother and son. If you kill Papyrus, Undyne [[OOCIsSeriousBusiness drops the monologues]], and coldly promises to kill you. The only character who cares about [[LivingEmotionalCrutch Papyrus]] more is [[spoiler: [[StepfordSmiler Sans]].]] She also cares very much about the Snowdin Canine Unit and Guards 01 and 02.
** [[spoiler: Asgore]] also fits. He trained Undyne himself from her childhood and is very caring towards her (and pretty much everyone). [[HundredPercentAdorationRating There isn’t a single monster who dislikes him]], except for [[AccuserOfTheBrethren Toriel]].

*** If you halt a No Mercy run at the last moment before fighting him, he'll say that he can tell you didn't strike him down with complete hatred, and is glad to see that you won't [[spoiler: destroy humanity or hunt down Alphys like he had feared you would]].
** Asgore: On a neutral run where [[spoiler: Flowey doesn't kill him first and he kills himself so that you can take his soul]], he'll regretfully tell you that he's sorry he couldn't give you a happy ending, but that you going free is what [[spoiler: his son Asriel]] would have wanted.
** [[spoiler: Sans]]: He'll say that he warned you what would happen and slowly staggers off-screen, saying that he's going to Grillby's. He then asks [[spoiler: Papyrus if he wants anything]] before you hear the sound if him turning to dust.

* FlowerMotifs: ''Golden Flowers,'' or ''Buttercups'' are a symbol of memory and death- [[spoiler: they are the flowers from their village that the first fallen human wanted desperately to see while on their deathbed, and buttercups are what they used to poison themselves with.]] They are found in the Royal Gardens (where you confront Asgore, who you must kill and take the soul of to leave the Underground), in Toriel's house (where they are heavily implied to be kept to honor the memory of [[spoiler: her two dead children]]), the entrance to the Ruins (what cushions the player's fall when they enter the symbolic 'underworld' of the game) and the dump (what [[spoiler: Flowey uses to save the player from falling to their death after remembering the first meeting with the Fallen Human in similar circumstances]]. And of course, Flowey himself is one- [[spoiler: a creature created after Asriel's death with all his memories but nothing else]].
* FoolishSiblingResponsibleSibling: Subverted with Papyrus and Sans. Papyrus appears to be an ambition-minded skeleton dedicated to serving the royal guard, while Sans only seems interested in pranks and [[LazyBum loafing]]. The reality is that Papyrus' attempts to be serious and mature makes him come across as quite goofy. He also doesn't have a single [[{{Pun}} mean bone]] in his body; Papyrus is incapable of actually hurting anyone and consequently isn't cut out for joining the royal guard. Meanwhile, Sans secretly spends a lot of his time trying to keep his brother happy and is quite [[SadClown cynical and melancholic beneath his goofy surface]], and he hides his own problems to not worry his brother. [[spoiler:If the player kills enough monsters, he eventually attempts killing them, and unlike his brother he will not show any mercy.]]

* {{Foreshadowing}}: [[Foreshadowing/{{Undertale}} As a story based game, Undertale has its own page for this trope]].

** ZigZagged with Toriel and [[spoiler:Asgore]]. She's still angry with him for [[spoiler:declaring war on humans in the Underground and killing six children that she had tried to protect, since he only needed one soul to cross the barrier and obtain six more.]] He doesn't blame her one bit for feeling this way. On the other hand, [[spoiler:she does save him from you in the True Pacifist ending and they work together at a school in the GoldenEnding]].

** '''The Realist''': Alphys. How she acts depends on which path you're taking. She'll either consider you friendly and a kind person or a nightmare and that she avoids having to meet you in person and helps all the monsters to escape from your reach.

** The four ghosts fit too : [[TheVoiceless Dummy]] (phlegmatic), [[TheEeyore Napstablook]] (melancholic), [[HairTriggerTemper Mad Dummy]]/[[spoiler:[[ClingyJealousGirl Mew Mew]]]] (choleric) and Napstablook's disappeared cousin [[spoiler:[[LargeHam Mettaton]]]] (sanguine).

** This even managed to sneak itself into the merchandise, if you buy Fangamer's "determination" bundle, Flowey will appear and offer you a one dollar discount. [[spoiler:It's treated like a DealWithTheDevil: if you accept it, the postcard that comes in the box, which is normally [[http://66.media.tumblr.com/e4ef368e9b7a8eaf90ae80454563dd62/tumblr_inline_o30a0mBQup1qda68o_500.png a detailed photo from one of the Pacifist endings]], is replaced with [[http://66.media.tumblr.com/90fef4e4bb250a0c7a9a7558e737d235/tumblr_inline_o309zxm29Y1qda68o_500.png the Soulless Pacifist ending's version in horrifying detail]]. Hope that one dollar you saved was worth it.]]

** In the game's release trailer, Undyne is shown hunting the player, captioned with "And strong enemies." [[spoiler:"..?" Is tacked on just before transitioning to the next scene, as she can be befriended over the course of the game.]]

* FriendlyNeighborhoodVampire: Apparently, [[spoiler:humans and monsters lived in harmony once long ago, and do again at the end of a Pacifist run]]. Think about all the monsters you meet (including ghosts, skeletons, wolf-people, giant talking octopii, and think of how people would react.

** Sans and Undyne interact even ''less'' with each other, the only time where they are seen together is when Undyne is chasing you through Hotland, seeing Sans sleep and getting annoyed for not helping her, in some of the Neutral endings where both of them survive, and [[spoiler:in the Pacifist ending when all the main monsters are together.]]
** Also Sans and Alphys never interact much, though late in the game it is revealed that they ''do'' know each other, since she is familiar with his humor, but whatever this connection is, the game doesn't elaborate on it.

* AChatWithSatan: [[spoiler: The Fallen Child]]. They are Frisk’s ShadowArchetype and seem to think they know your dark side quite well. They do give a test of character of sorts with the ERASE or DO NOT choice, as well as the choice to [[DealWithTheDevil sell your soul]]. If that wasn’t enough to convince you, they even call themself “the demon that comes when people call [their] name” if you complete two Genocide Routes.

** During their lunch date, Sans will tell the player that Papyrus claims a flower occasionally appears to him and tells him secrets and predictions. While Sans assumes that someone is playing a trick on Papyrus using an Echo Flower, [[spoiler:the "flower" is, of course, Flowey. And who tells Papyrus to gather everyone in one place at the end of the Pacifist route so he can absorb all their [=SOULs=]...?]]

** Flowey appears twice in the ruins and then disappears from the rest of the game aside from a few EasterEggs. [[spoiler:At the end of the game, he kills Asgore and steals the human SOULs, completing his master plan and revealing himself to be the true [[BigBad Big Bad]] of the game]].

* CloseKnitCommunity: The Underground is this — everyone knows each other (with the exception of monsters residing in the Ruins, since the entrance sealed off from the rest of the Underground; only Napstablook can travel between them freely), and everyone cares deeply for each other. If you kill even one NPC, no matter how minor, people ''will'' notice and care. It's probably inevitable it turned out this way; most of the monsters' population was wiped out in the war, and the few who remain are all stuck in the same relatively small area for the foreseeable future. If ''that'' won't force you to get to know your neighbors...

* ComicRolePlay: En route to the GoldenEnding, the player will find themself [[spoiler:on a date with Alphys. She admits that she likes Undyne, but can't work up the nerve to tell her. The player [[ButThouMust suggests]] that they roleplay as practice, and then chooses between serious or goofy role-playing lines. Of course, it spirals out of control regardless of the player's choices.]]

** An in-universe example. [[spoiler:Flowey closes the game]] before you can stop him from [[spoiler:using the human [=SOULs=]. When you boot the game up again, he has already changed the world to eliminate all other threats and replaced your file with his, which is at LV 9999 despite the highest reachable LV being 20. He then literally shatters that file, before you can overwrite or delete it. At the beginning of the fight, he makes a quicksave. Throughout the fight, he makes quicksaves right before attacking so he can unexpectedly load them later, but loading them doesn't give you back any of your health. When you finally beat him, he loads his first save, thus undoing all of your progress. (Or so he ''thinks''....)]]
** Another in-universe example: [[spoiler:Asgore gets the first turn and uses it to destroy the MERCY button.]]
** Even worse, [[spoiler:Sans gets the first turn, attacks you on the menus by exploiting the fact that your [=SOUL=] is the cursor, completely ignores mercy invulnerability, and dodges your attacks. He's so good at reading people's faces that he can tell if you've died to him before and he exploits this knowledge by [[TalkToTheFist interrupting his own dialogue at varying points to attack you.]]]]

** During part of the [[spoiler:pacifist TrueFinalBoss, you are unable to select any menu option except Act->Struggle, which just says "Can't move your body." Attacks during this phase are almost impossible to dodge, but it also doesn't matter how many times you get hit.]]

* ConvectionSchmonvection: Zigzagged. While Undyne's armor heats up significantly while crossing a bridge over lava, to the point where she passes out, you are perfectly fine in that same area and suffer no heat related issues, even when you make it ''hotter'' to appease a monster. Then again, Undyne is a ''fish monster'' wearing heavy steel armor. Your character is wearing a simple striped shirt. Also, the Royal Guardsmen apparently have "cooling dirt" on their armor, which you need to polish away in order to get one of them to succumb to the heat and take his armor off as well. Since Undyne is normally stationed in Waterfall, her armor would have no need for such enhancement.

** If you make certain choices, [[spoiler:Sans will say he understands that you might have been defending yourself, but then he asks you if a person with a special power has a responsibility to use it to help people. If you say yes, his eyes go dark and he asks why you killed his brother, then disappears.]]
* CringeComedy: The date with Alphys on the Pacifist route. Between Alphys's complete lack of social skills, and the fact that she's obviously pining for Undyne, it's awkward from the word "go." But then you start to roleplay an interaction between Alphys and Undyne, and things get even worse. (Or better, since that's when the scene goes from amusing to ''hilarious''.) ''And then Undyne overhears you.''

** At the end of the [[KillEmAll No Mercy]] route, [[spoiler:you get to butcher Flowey repeatedly into smaller and smaller pieces until he's totally gone.]] Considering most fights end with a clean kill, be it from massive damage or a sneak attack, this is easily the most brutal way to die in the entire game.

* CruelTwistEnding: If you follow a No Mercy run with a Pacifist run. [[spoiler:Everything seems to be normal... [[SuddenDownerEnding up until the last moment]], in which it's revealed that the player character has been possessed by the Fallen Child and is then implied to destroy everyone and everything within the game, apart from themself and the player character.]]

** As you can learn throughout the game, the war that the humans won against the monsters was one of these. In fact, [[spoiler:not a single human was killed during the war. This makes sense when you consider that Frisk, who is a mere child, can completely eradicate the monster population single-handedly, and it's likely that adult warriors and soldiers probably fought in the war itself. Combine that with the knowledge that a human's killing intent and prior killing history makes them even deadlier to monsters, and it's no shock that seasoned, experienced soldiers were able to almost effortlessly wipe out most of the world's monsters.]]

* DarkHorseVictory: If you kill ''only'' all the "Boss" characters like Toriel, Papyrus, etc., but spare every other encounter, then [[spoiler:the Annoying Dog somehow manages to become president of the Underground, and Sans comments that "Somehow, everyone seems happier this way".]]

** Zigzagged with Flowey's theme, "Your Best Friend", which turns into "Your Best Nightmare", a manic, distorted, utterly insane version when [[spoiler: Flowey becomes Photoshop Flowey]]. However, it's eventually replaced with "Finale", a more hopeful version, once the player is finally able to start getting the upper hand on [[spoiler:Photoshop Flowey]].
** Due to very different tempo and instrumentation, it's not obvious, but "Battle Against a True Hero" (heard when fighting Undyne in the No Mercy route) uses a melody which is very similar to "Spear of Justice" (Undyne's usual battle theme in Neutral and Pacifist Runs). The similarity is due to the fact that "Spear of Justice" showcases Undyne as a HotBlooded, bombastic warrior who is filled with undue enthusiasm about attacking you, while "Battle Against a True Hero" shows the same character in a more solemn, serious state as [[spoiler:a heroine trying to hold out hope in the face of unspeakable evil that seriously threatens to plunge everything into death and despair.]]

** The [[PlotTriggeringDeath Plot-Triggering Deaths]] are a tragic example: [[spoiler: Asriel Dreemurr and the first Fallen Human]] were both little kids when they died.

* DeconstructorFleet: Though not immediately apparent, the game is a {{Deconstruction}} of [=RPGs=], both on a superficial level from sarcastic flavor text and characters (staying in the Snowed Inn, for example, has the innkeeper give your money back, mentioning you were only up there for two minutes) as well as the deeper plot. It also examines OneHundredPercentCompletion on a meta level. What if there were alternate ways of getting from Point A to Point B, and the person going through the motions happens to have the ability to go back and explore these routes after going through one? What if they remember going through the motions? What if someone else can remember what they did in a previous loop? If the world inside the game is real, what happens to it when the player reloads a save, or starts NewGamePlus? It also takes a look at a number of gaming tropes, like the Determinator, SaveScumming, TurnBasedCombat, LevelGrinding, and, most of all, VideoGameCrueltyPotential. [[spoiler:And, for the ''truly'' curious, DummiedOut.]]

** Monsters are always monochrome in battle, but are colored on the overworld. [[spoiler:This is because all monster [=SOUL=]s are grey.]] The one exception is Froggit, which is the same color in both the overworld and in battle. The monochrome battle sprites are averted in a few cases, such as Toriel’s eyes and [[spoiler: Sans’...blood?]]

* FantasticAesop:
** The Genocide route is extremely unrelenting in hammering the point home you're likely only taking that route to see what happens, rather than any actual desire to hurt or punish the characters, and the few characters who are aware that [[spoiler:you're able to effectively time travel using the ability to SAVE]] argue the fact you can undo everything doesn't make you any better of a person. However, the only reason their point sticks is because the Genocide route ends with an all but literal DiabolusExMachina in the form of [[spoiler:the Fallen Child, who destroys the world whether you want to or not and then only allows you to recreate it if you [[DealWithTheDevil sell your SOUL to them]]]]. Doing so prevents you from ever achieving the GoldenEnding, as [[spoiler:the child takes you over in the final scene of the Pacifist route and is implied to kill everyone again anyway]]. So in some ways, it's an Arbitrary Rules Aesop about [[spoiler:DemonicPossession and [[DealWithTheDevil deals with the devil]]]], but since its primary purpose is to drive the point the other characters are making, it makes you wonder how effective their point would have been without [[spoiler:the Child's cross-timeline possession of you]].
** Less {{Anvilicious}}ly, the fact that the GoldenEnding can only be achieved by refraining from committing the CrimeOfSelfDefense no matter how violent your enemy is only makes sense in-universe because the barrier needs seven human souls worth of power to be destroyed; the six human souls in reserve plus ''nearly every monster in the Underground'' conveniently make up the correct amount, and you can't do it with one iota less. It's a pretty convenient coincidence that this is the number of monsters currently alive, and the fact that almost every living monster soul adds up to one human soul is only mentioned on one PamphletShelf.

** The four monsters you befriend in the Pacifist route. [[SmallNameBigEgo Papyrus]] (sanguine), [[HotBlooded Undyne]] (choleric), [[NervousWreck Alphys]] (melancholic), and [[TheSlacker Sans]] (phlegmatic). [[TheCommicallySerious The Human Child]] is the leukine.

** The four monsters you befriend in the Pacifist route. Papyrus (sanguine), Undyne (choleric), Alphys (melancholic), and Sans (phlegmatic). The Human Child is the leukine.
** The four ghosts fit too : Dummy (phlegmatic), Napstablook (melancholic), Mad Dummy/[[spoiler:Mew Mew]] (choleric) and [[spoiler: Mettaton]] (sanguine).
** The royal family can count as well: the King Asgore Dreemurr (phlegmatic), the former Queen[[spoiler:, Toriel]] (melancholic), the [[FallenPrincess Fallen Prince]] Asriel (choleric), and [[spoiler:the First Human]] (sanguine).

* FragileSpeedster: If you keep the Bandage on, you'll have no additional defense whatsoever, but you'll be guaranteed to be able to run from any encounter that gives you the option.

* CustomBuiltHost: Mettaton is a performing robot built by Alphys, but is actually [[spoiler: a ghost-like monster, implied to be a cousin to Napstablook and Mad Dummy, possessing a mechanical body Alphys built for them so they could live out their dreams of being a star to monster-kind.]]

** When you reach the Last Corridor on a Pacifist run, save the game before you talk to Sans. As soon as you stop talking to each other, reload the game and talk to him again. Keep doing this until you get the key to his room. Search his room for a silver key to the [[BehindTheBlack door behind his house]]. There's a secret lab with what is possibly a time machine there.

** There's a hidden encounter in Hotland. Follow the path from the Right Floor 2 elevator until you reach the long, straight area with a T-intersection. There's an invisible path going north. Go there when your computer's time and date are set for October 10th at 8 PM[[note]][[/note]] to encounter So Sorry.

*** When you restart the game after [[spoiler:Flowey forcibly closes it and the intro glitches out]], the title cycles through random gibberish. It then reads [[spoiler:"Floweytale"]] until you defeat that boss.

** The demo allows the player to earn EXP by lowering monsters' health before sparing them, while in the final game, it can only be earned by killing them. [[spoiler:Since EXP stands for Execution Points, it wouldn't make sense to be able to earn any without killing anything.]] Vegetoids in the demo also must be spared by attacking them first, and the "Devour" ACT will kill them outright; in the final game they can be spared through [=ACTs=] like every other monster and "Devour" never harms the Vegetoid.

* AChatWithSatan: [[spoiler: Chara]]. They are Frisk’s ShadowArchetype and seem to think they know your dark side quite well. They do give a test of character of sorts with the ERASE or DO NOT choice, as well as the choice to [[DealWithTheDevil sell your soul]]. If that wasn’t enough to convince you, they even call themself “the demon that comes when people call [their] name” if you complete two Genocide Routes.

* EarlyInstallmentWeirdness: The Kickstarter videos have some different characterizations from the actual game. Sans is seen closing his mouth to drink lemonade, while he ''never'' closes his mouth in the game, sporting a goofy grin at all times. Toriel is also shown manifesting lemonade in thin air, though the only magic she's shown to have in the game is fire magic.

* EarnYourHappyEnding: On the other hand, if you spared every enemy and got to the final room with no kills? Not only did you not increase your LV (meaning you beat the game on the starting 20 HP), you still don't get the good ending unless you've befriended everybody. Then after that, you go through the True Lab, and find out the secrets of the hidden lab, as well as the truth of Flowey's existence, followed by another boss battle. The other monsters also get their happy endings:

** If you do nothing but hum when facing [[UniqueEnemy Shyren]], this will have a mini-plot where you and she improve your singing careers. In game, this means you can cause Knight Knight to fall asleep faster by singing. This also activates Shyren's yellow title in the epilogue.
** Each character in the ending credits / epilogue has two descriptions. The first is a standard white description, and the second is a yellow description if you did something unique with them. One of the most obscure is Aaron's, which is triggered by wandering around the lake near Napstablook's house while playing one of their music [=CD=]s.

** There's a hidden encounter in Hotland. Follow the path from the Right Floor 2 elevator until you reach the long, straight area with a T-intersection. There's an invisible path going north. Go there when your computer's time and date are set for October 10th at 8 PM to encounter So Sorry.

** By changing a property in the ''Undertale.ini'' file, you can have some extra Fun with the game by hunting for secrets. However, should you get the Wrong Number Song to happen, then don't expect any Fun. This was later patched so the Fun value no longer needs to be modified to cause this.

*** When you restart the game after Flowey forcibly closes it and the intro glitches out, the title cycles through random gibberish. Until you beat him, it reads "Floweytale".
*** If you finish a No Mercy run, the game has no title after the Fallen Child destroys the world.
** Related to the above: when the Fallen Child attacks the game itself and fills the screen with 9s, the window shifts and shakes repeatedly.

* DueToTheDead: With monsters, this trope is a bit difficult to do since the monsters, when they die, turn into dust, and for this reason [[spoiler:Alphys accidentally infused a flower with Asriel's remains, trapping him in that state]]. For humans, however, their bodies notably don't dissolve, so [[spoiler:Asgore and Toriel show a lot of respect for the corpses even as Asgore takes their souls in preparation to break the barrier. Toriel also took the Fallen Child's body and buried it in a field of golden flowers, the field on which Frisk lands]].

** Asgore: On a neutral run where [[spoiler: Flowey doesn't kill him first and he kills himself so that you can take your soul]], he'll regretfully tell you that he's sorry he couldn't give you a happy ending, but that you going free is what [[spoiler: his son Asriel]] would have wanted.

* CuttingTheKnot: The second "X's to O's" puzzle is more difficult than than the others and can be frustrating to figure out. However, a nearby tree has a hidden switch that immediately solves the puzzle when you press it.

** spoiler:When Alphys reveals that it takes at least [[spoiler:a human SOUL and a monster SOUL]] to cross the barrier, she laments that in order for you to leave, you'd have [[spoiler:to kill Asgore]]. Toriel is also aware of the minimum amount of power needed, which she points out to Asgore that he could've freed everyone easily years ago if he [[spoiler:just used ''one'' SOUL to leave and find the rest outside, since Alphys's fact also works in ''reverse''.]]

* EvolvingMusic: As you befriend more and more characters, the title screen's music becomes more lively as more and more instruments are added in. [[spoiler:Completing the True Pacifist run and seeing the epilogue makes it go quiet.]]

* FourTemperamentEnsemble: The four monsters you befriend in the Pacifist route. Papyrus (sanguine), Undyne (choleric), Alphys (melancholic), and Sans (phlegmatic). The Human Child is the leukine.

** [[spoiler:Upon defeating Asgore, Flowey steps in to absorb the six human souls, which causes the game to abruptly quit. Upon starting the game back up, things only go downhill from there.]]
** [[spoiler:Also part of Flowey's M.O. since he also has the power of DETERMINATION. Flowey routinely jabs at you for cruel actions and laughs if you try to use the save system to wipe them clean. His biggest threats to you are also to destroy your save file and reset the game to the beginning.]]
** The game dives into this full force at [[spoiler:the end of the No Mercy run. The boss tries to convince you to stop playing, and things get even worse in the ending itself]]. And it gets even ''worse'' than that if you [[spoiler:try to restart the game after that]].

** Inverted in the genocide route, as some characters will express fear of ''the player''. For example, [[spoiler:after Flowey's monologue in New Home, he realizes that he's the player's next target. Sans also knows about the player, and it is revealed that he has lived most of his life simply accepting everything the player does, knowing that they will eventually reset anyway]].

* FriendlyNeighborhoodVampire: Apparently, [[spoiler:humans and monsters live in harmony, and still do at the end. Think about all the monsters you meet, and think of how people would react]].

* ComedyAsAWeapon: Snowdrake can be spared after laughing at his jokes, and monsters with him can be spared after making your own joke.

** [[spoiler:A distorted, solemn version of the Snowdin theme plays while "fighting" one of the monsters Alyphys injected with Determination, who is really the mother of an enemy from that area.]]

** [[spoiler:Zigzagged with Flowey's theme, "Your Best Friend", which turns into "Your Best Nightmare", a manic, distorted, utterly insane version when Flowey becomes Photoshop Flowey. However, it's eventually replaced with "Finale", a more hopeful version, once the player is finally able to start getting the upper hand on Photoshop Flowey.]]
** Due to very different tempo and instrumentation, it's not obvious, but "Battle Against a True Hero" ([[spoiler:heard when fighting Undyne in the No Mercy route]]) uses a melody which is very similar to "Spear of Justice" ([[spoiler:Undyne's usual battle theme in Neutral and Pacifist Runs]]). The similarity is due to the fact that [[spoiler:"Spear of Justice" showcases Undyne as a HotBlooded, bombastic warrior who is filled with undue enthusiasm about attacking you, while "Battle Against a True Hero" shows the same character in a more solemn, serious state as a heroine trying to hold out hope in the face of unspeakable evil that seriously threatens to plunge everything into death and despair.]]

* DatingSim: Papyrus's sidequest includes a style parody of them. [[spoiler:Alphys's looks like it's going to be a call back to this, but it's a bait and switch.]]

** [[spoiler:New Home is a colorless shade of white and grey, the only color in sight being the golden flowers scattered around the house area. This is presumably meant to represent how lifeless Asgore's world has been since the death of his children.]]

** If you dispatch Toriel in a particularly cruel way, she'll declare that you're worse than the monsters. [[spoiler:Either slay as many monsters as you can, or get her to back down and then attack her.]]